In the related art, when driving a brushless motor, a motor drive apparatus sets a mechanical advanced angle to 0 degrees, changes the advanced angle on a software, and drives the brushless motor. Specifically, the motor drive apparatus acquires a sensor signal that corresponds to each of a U-phase, a V-phase, and a W-phase of the brushless motor from a detection sensor (for example, a Hall IC) that detects a rotation position of a motor.
Then, the motor drive apparatus recognizes a stage number on the basis of the acquired sensor signal, reads out a power distribution pattern that corresponds to the stage number, performs shifting by a predetermined rotation position (for example, an electric angle of 30 degrees), and then, by performing a PWM control on a switching element that constitutes an inverter circuit in accordance with the power distribution pattern that is read out, drives the brushless motor.
In a low-speed rotation time of the brushless motor, the interval between sensor signals that are output from the detection sensor is large, and therefore, the motor drive apparatus cannot change the advanced angle and drives the brushless motor at an advanced angle of 0 degrees. However, when driving the brushless motor at an advanced angle of 0 degrees, a counter electromotive voltage due to regeneration is generated. In this case, in a power distribution phase, the motor drive apparatus can allow the counter electromotive voltage to escape toward an electric source side, and therefore, it is possible to prevent a voltage from being increased; however, in a non-power distribution phase, the switching element is in an OFF state, and therefore, a voltage increase is caused. Therefore, the motor drive apparatus may recognize the voltage increase due to the counter electromotive voltage as an abnormal voltage increase occurring and may stop driving the brushless motor for the purpose of protecting an erroneous operation or the failure of circuit components.
In order to allow the counter electromotive voltage that is generated at the non-power distribution phase to escape toward the electric source side, a method of performing a so-called non-free rectangular wave drive is considered in which a power distribution of a predetermined duty ratio is performed to the non-power distribution phase, and a voltage that corresponds to a neutral point is generated. Thereby, by the motor drive apparatus performing the non-free rectangular wave drive, the non-power distribution phase disappears, and it is possible to prevent the voltage from being increased due to the counter electromotive voltage. However, when a current phase becomes later than the advanced angle of 0 degrees by rotating the brushless motor at a high speed, the amount of the counter electromotive voltage is increased. In this case, it is not possible to prevent the voltage from being increased even when performing the non-free rectangular wave drive described above, and there is a possibility that the brushless motor may be stopped.
As a method of reducing this current phase delay, there is a method in which the advanced angle is mechanically shifted, for example, by 30 degrees, and in a reverse rotation time, the stage number (that is, power distribution pattern) is shifted by one on a software. For example, when the advanced angle is mechanically shifted by 30 degrees in a normal rotation direction, a delay angle is shifted by 30 degrees in a reverse rotation direction. A three-phase brushless motor has totally six power distribution patterns, and therefore, by shifting the power distribution pattern by one in a reverse rotation time, an advanced angle of 60 degrees that is an advance of an amount corresponding to one stage number occurs at the delay angle of 30 degrees. As a result, the angle is an advanced angle of 30 degrees even in the reverse rotation time, and it is possible to impart an advanced angle of 30 degrees to both rotations. Therefore, even when the current phase delay occurs, a delay angle does not occur, and it is possible to dissipate the effect by the counter electromotive voltage.
An advanced angle control and a delay angle control of a motor drive apparatus of the related art are described with reference to FIG. 6. FIG. 6 is a view showing a control method of a motor drive apparatus of the related art. Part (a) of FIG. 6 is a view showing a control method of an advanced angle control of the motor drive apparatus of the related art. As shown in part (a) of FIG. 6, the motor drive apparatus of the related art counts time for a certain period of time using a timer on the basis of a previous sensor signal and advances the angle by performing power distribution to a coil of any one of the U-phase, the V-phase, and the W-phase when the time counting is completed. For example, the motor drive apparatus starts a time counting of a certain period of time using the timer at a rising timing of the sensor signal corresponding to the U-phase and performs power distribution to a W-phase coil at a timing when the time counting of the certain period of time is completed. However, an advanced angle of 30 degrees is mechanically added, and therefore, in the advanced angle control of the related art, it is possible to drive the brushless motor only at an advanced angle of 30 degrees or more. Therefore, since it is not possible to perform driving, for example, at an advanced angle of 15 to 20 degrees (power distribution angle of 130 degrees) which is an advanced angle of 30 degrees or less, there is a problem in that it is not possible to adjust the advanced angle, and an operation sound, a radio wave noise, and the like when mounted on an actual vehicle are degraded. In order to solve this problem, there is a method of performing a delay angle control and thereby driving the brushless motor at an optimum advanced angle.
Part (b) of FIG. 6 is a view showing a control method of a delay angle control of the motor drive apparatus of the related art. The motor drive apparatus starts a time counting of a certain period of time by a timer that is provided on a microcomputer at rising and falling timings of each sensor signal and performs power distribution to a coil of each phase at a timing when the time counting of the certain period of time is completed. For example, the motor drive apparatus starts a time counting of a certain period of time by the timer that is provided on the microcomputer at a rising of a U-phase sensor signal and performs power distribution at a negative voltage to a W-phase coil at a timing when the time counting of the certain period of time is completed. The motor drive apparatus starts a time counting of a certain period of time by the timer that is provided on the microcomputer at a falling of the U-phase sensor signal and performs power distribution at a positive voltage to the W-phase coil at a timing when the time counting of the certain period of time is completed.